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    <script>
        //实例化 Promise对象
        const p=new Promise(function(resolve,reject){
            setTimeout(function(){
                //
                // let data='数据库中的数据';
                // //resolve
                // resolve(data);

                let err='数据读取失败';
                reject(err);
            },1000);
        });

        //调用Promise对象的 then 方法
        p.then(function(value){
            console.log(value);//成功
        },function(reason){    //失败
            console.log(reason);
        })
    </script>
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